Optical Fibres
4 marks · NormalThe diagram below shows a simplified optical fibre.
Label the core and cladding on the diagram.
Draw a path to show how light travels along the optical fibre, reflecting from the core–cladding boundary.
Explain why the light remains in the core as it travels.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) core (inner), cladding (outer, dashed) · must show labels placed on correct circles
(b) light ray drawn zigzagging between the core–cladding boundary · must show light path reflects at boundaries at shallow angle
(c) Because total internal reflection occurs at the core–cladding boundary. · must show states total internal reflection
Must show: core and cladding correctly labeled; light path reflects at boundary; reason is total internal reflection
Common mistakes: Labeling swapped; forgetting reflection angle.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Core and cladding correctly labeled on diagram.
B1 (b) · 1 mark · Light path drawn correctly showing at least one reflection at the core–cladding boundary.
B1 (b) · 1 mark · Path stays within core and shows typical zigzag.
B1 (c) · 1 mark · States that total internal reflection keeps the light in the core.
Worked solution
a) The inner solid circle should be labeled 'core', and the outer dashed circle labeled 'cladding'. b) The light path should be drawn as a zigzag line inside the core, reflecting at the inner surface repeatedly. c) The light remains in the core because it is totally internally reflected at the core–cladding boundary.